1. Field of the Invention
This invention relates to a semiconductor light emitting device having a ZnSSe layer and a method for manufacturing the same.
2. Description of the Prior Art
Among light emitting devices employing Group II-VI compounds, a device using ZnSSe has been considered by many to be a promising blue-emitting device
Many attempts have been made to form a light emitting device through the various growth methods, for example, liquid phase epitaxy ion implantation following the annealing, of a ZnSSe crystal. However, no practical device has been achieved using these conventional methods. The main reason for this is that, when an impurity doping is performed in accordance with the conventional method, vacancies are produced, which cancel the effect of such an impurity doping,--known as what is called "self compensation effect"--so that better control cannot be made with respect to the conductivity type.
In the field of the light emitting devices, attention has recently been paid to a metalorganic chemical vapor deposition (MOCVD) method, which is a vapor growth mehtod using organometallic compounds. The process for manufacturing a light emitting diode (LED) and a laser diode (LD) employing Group III-V compounds has reached a stage of practical application. When a ZnSSe crystal is grown on a compound, by means of the MOCVD technique, it has been found that the ZnSSe crystal layer whose lattice parameter is matched to that of GaAs has a specular surface as smooth as that of the substrate, and X-ray diffractometric analysis has shown that it has a better crystallinity (full width at half maximum&lt;40").
It is expected that the MOCVD technique enables crystal growth under the thermally non-equilibrium condition and then suppresses the self-compensation effect at a low growth temperature. Many experiments have been tried to grow a ZnSSe crystal with a pn junction on a GaAs substrate. However, no satisfactory pn junction of ZnSSe has yet been formed even if the MOCVD process is employed. From impurity analysis of ZnSSe crystal it has been found that a greater amount of Ga is diffused from a GaAs substrate through the ZnSSe crystal layer and that the donor and acceptor impurities diffused mutually through the pn junction. It has also been found that light emission intensity related to deep levels increased due to the doping of the donor and acceptor impurities.
As set forth above, while a ZnSSe crystal layer of excellent crystallinity can be formed on the Group III-V compound substrate, by use of the MOCVD method, it has however proven difficult to form a pn junction of better characteristic in the ZnSSe crystal layer.